A frequent cause of accidents in street traffic is that the driver overlooks another vehicle located in the blind spot during a lane change or when cornering. To reduce this danger, warning systems have been developed, which are capable of detecting objects in the blind spot with the aid of a ranging sensor, identified here as the main sensor, and outputting a warning indication to the driver, for example, in the form of a visual display in the outside mirror for the affected vehicle side. If necessary, an acoustic warning signal may also be output if the intention of the driver to change lanes or corner is recognized based on the status of the turn signal and/or the steering movements.
Such warning systems are also referred to as BSD (blind spot detection) systems. In such systems, a short-range radar sensor (SRR), such as a pulse radar, a lidar sensor, or an ultrasonic sensor, is frequently used as the sensor. Typically, these sensors execute only a distance measurement and do not have any angular resolution capabilities, so that only restricted information is available about the precise position and the movement state of the detected object. Incorrect warnings may thus occur easily, which lower the driver's trust in the system.
A warning system of this type is described in published German patent document DE 101 25 426, in which system, in addition to the main sensor which is located on the vehicle side to be monitored at the rear vehicle corner, a second ranging sensor is provided on the front vehicle corner, so that through the combined detection ranges of both sensors, the entire area of the neighboring lane is monitored at the side of the host vehicle, as well as slightly in front and behind. Through an analysis of the time curve of the distance values periodically measured by the two sensors, it may then be ascertained whether the detected object is moving in the same direction as the host vehicle or in the opposite direction, or whether the detected object is a stationary object. In this way, incorrect warnings which are caused by oncoming traffic or by stationary objects such as traffic signs, guide rails, and the like, may be prevented.
Incorrect warnings may, however, also be triggered by objects which move in the same direction as the host vehicle, for example, by a following vehicle which follows the host vehicle in the same lane and approaches so closely that it reaches the detection range of the rear sensor. In order to avoid such incorrect warnings, until now the main sensor has been configured and positioned in such a way that its detection range is directed diagonally to the rear on the neighboring lane, so that following vehicles are normally not detected. However, in curves or in cases in which the following vehicle drives somewhat offset to the host vehicle, the following vehicle may still reach the detection range and thus trigger an incorrect warning.